Apparatus for accelerating cathode heating

ABSTRACT

Apparatus for accelerating the heating of the cathode heater of a cathode ray tube or the like. A first self-heating positive temperature coefficient resistor is interconnected to an electrical power source. Positioned in heat-exchange relationship with the first resistor is a second self-heating positive temperature coefficient resistor. A resistor of substantially fixed resistance is shunt-connected with said second self-heating resistor. These shunt-connected resistors are connected in series with the heater of the cathode across an electrical power source which supplies power of a substantially constant potential in excess of that required to maintain the heater of the cathode at a predetermined temperature. After power is initially supplied to the cathode heater, its potential will be reduced from a level substantially in excess of that required to maintain the heater at the predetermined temperature to a level which maintains the heater at substantially that predetermined temperature.

United States Patent [1 1 Berg [ APPARATUS FOR ACCELERATING CATHODEHEATING [75] Inventor: Peter G. Berg, Norton, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[22] Filed: July 1, 1974 [21] Appl. No.: 484,539

[52] US. Cl. 315/94; 315/8; 315/100; 315/107; 315/309; 317/1575; 328/270{51] Int. Cl. H051) 39/00 [58] Field of Search 315/94, 99, 100, 106,107, 315/112, 114, 116,119,149, 179,192, 309, 311, 8; 313/153; 328/270;317/157.5 TV

l l May 27, 1975 Primary ExaminerR. V. Rolinec Assistant ExaminerE. R.LaRoche Attorney, Agent, or Firmlames P. McAndrews; John A. Haug; EdwardJ. Connors, Jr.

[57] ABSTRACT Apparatus for accelerating the heating of the cathodeheater of a cathode ray tube or the like. A first selfheating positivetemperature coefficient resistor is interconnected to an electricalpower source. Positioned in heat-exchange relationship with the firstresistor is a second self-heating positive temperature coefficientresistor. A resistor of substantially fixed resistance isshunt-connected with said second self-heating resistor. Theseshunt-connected resistors are connected in series with the heater of thecathode across an electrical power source which supplies power of asubstantially constant potential in excess of that required to maintainthe heater of the cathode at a predetermined temperature. After power isinitially supplied to the cathode heater, its potential will be reducedfrom a level substantially in excess of that required to maintain theheater at the predetermined temperature to a level which maintains theheater at substantially that predetermined temperature.

4 Claims, 4 Drawing Figures 9 T/ p/ g APPARATUS FOR ACCELERATING CATHODEHEATING BACKGROUND OF THE INVENTION This invention relates to apparatusfor acceleration of cathode heating and more particularly to apparatusfor providing rapid warm-up of the cathode heater of a cathode ray tubesuch as used in a television receiver or the like.

With the advent of solid-state circuitry in television receivers. theaudio or sound portion of the program would be immediately heard but thetime period required for the cathode heater of the picture tube to bebrought up to its operating temperature delayed the video portion of theprogram for about seconds or so. In order to reduce this delay ofpicture presentation, such television receivers were provided withinstanton" circuitry which would provide a picture within about I secondor so. This was accomplished typically by maintaining a reducedpotential across the CRT cathode heater at all times while the receiverwas off so that the CRT cathode could be more rapidly warmed up when thereceiver was turned on.

While this instant-on circuit functions effectively to reduce the delayin video presentation, it is not without some substantial disadvantages.Not only is there a continuous power drain, which constitutes a seriousenergy waste, but the hazard of fires from such continuously partiallyenergized television receivers has raised widespread and deep concern.

SUMMARY OF THE INVENTION Among the several objects of this invention maybe noted the provision of apparatus for accelerating the heating of thecathodes of CRTs and the like so as to insure warm-up of the typical CRTcathode heater to provide video presentation within about 5-8 seconds,but which has no power drain when the receiver is turned off; theprovision of such apparatus which eliminates any fire hazard fromcontinuously partially energized receiver circuitry and which is low incost and reliable in operation; and the provision of such apparatuswhich utilizes no electromechanical contacts but employs solid-statedevices and provides a smooth application of electrical energy to thecathode heater thereby avoiding thermal shock.

Briefly, apparatus of the present invention includes a firstself-heating positive temperature coefficient resistor having arelatively low initial resistance which increases abruptly as itstemperature rises above a given level and means for interconnecting itto an electrical power source thereby rapidly to heat it above a givenlevel. A second self-heating positive temperature coefficient resistoris positioned in heat-exchange relationship with the first resistor andit, too, has a relatively low initial resistance which increasesabruptly as its temperature rises above a given level. A resistor ofsubstantially fixed resistance is shunt-connected with the secondself-heating resistor. Means are provided for interconnecting theseshunt-connected resistors in series with the heater of the cathodeheater of a CRT or the like across an electrical power source whichsupplies power of a substantially constant potential but in excess ofthat required to maintain the cathode heater at a predeterminedtempertture. The resistance of the second self-heating resistor ispreferably less, and at least not substantially more, than that of thefixed resistor at temperatures below its aforesaid given level but issubstantially greater than that of the fixed resistor at temperaturesabove its aforesaid given level. After power is initially supplied tothe cathode heater its potential will be reduced from a levelsubstantially in excess of that required to maintain the heater at itspredetermined temperature to a level which maintains the heater atsubstantially its predetermined temperature as the first and secondresistors self-heat thereby to increase and then maintain the secondresistor at a temperature above its aforesaid given level, and thusaccelerate the heating of the cathode.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a circuit diagram of apparatusof the present invention for accelerating the heating of the cathode ofa cathode ray tube;

FIG. 2 is a graphical representation of the voltagetime relationship forvarious values of applied voltage and shunt resistors utilizing a lowresistance load in the apparatus of FIG. 1;

FIG. 3 is a circuit diagram of another embodiment of this inventionwhich performs the additional function of degaussing of the televisionreceiver; and

FIG. 4 illustrates graphically the voltage applied to a CRT cathodeheater as a function of time when employing apparatus of this invention.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, aself-heating positive temperature coefficient (PTC) resistor P1 is shownconnected across an electrical power source V by means of a switch S andconductive leads. A second selfheating PTC, P2, is shunt-connected witha resistor R of substantially fixed resistance and these twoparallelconnected components are serially connected with an electricalload K constituted by a resistance, such as the filament or cathodeheater of a CRT or the like, across the electric power source V viaswitch S.

Self-heating resistors PI and P2 are each conventional PTC resistors,usually in the form of a pill, having a resistivity-temperature curvewhich is steepsloped above a threshold or anomaly temperature. Such PTCresistors are formed from certain doped barium titanates, orcarbon-black loaded cross-linked polyethylenes, etc. They have arelatively low resistance at usual ambient temperatures but afterinitial energization by a source of electrical power will self-heat andincrease their temperature and resistance. Heat will be generated andthe resistance will increase rapidly above the anomaly temperature untilthe heat generated balances the heat dissipated at which time thetemperature and resistance stabilize with the resistance many times theinitial value. Thus each PTC has a transition from a high heatgenerating state initially to a low heat generating state at an elevatedtemperature (e.g., C.-l 35C.) at which it tends to self-regulate. Thesetwo PTC resistors are positioned in heat-exchange relationship with eachother, such as by securing them to a common heat-conductive body, e.g.,as shown in US. Pat. No. 3,307,167.

When the apparatus of this invention is energized by closing switch S,the substantially constant potential of power source V1 is appliedacross the two parallel circuits respectively constituted by P1 and byP2,R series connected with load K. The potential of V1 is selected toexceed that required to maintain the current through load K at apredetermined level. A typical CRT cath ode heater is designed to bemaintained at its predetermined temperature when a voltage of about6.3V. is applied thereto. The resistance of such a cathode heater whencold is about 2 ohms but rapidly rises to a steadystate value of about5-7 ohms. PTC resistors are used which have a resistance at the usualambient room temperatures of about l-2 ohms. The resistance rapidlyrises as the unit self-heats above its threshold temperature and has aresistance at its stabilization temperature that is typically in theorder of about 40-200 or more ohms at voltages in the order of l 5V. asused in this example. A value of R is chosen so that the initialresistance of P2 is not substantially more than that of R. Preferably Rhas a resistance that somewhat exceeds that of P2 at ambient.

Referring now to FIG. 2, the operation of the apparatus of thisinvention is illustrated using a 7 ohm resistor as the load, a 120C. PTCresistor as P1 and an 80C. PTC resistor as P2. Curve A represents thevoltage applied across the 79. load where R is lO.lQ and V1 is 15.8V. Itwill be noted that after initial energization the voltage across theload drops from a little more than l3V. to about 6.3 volts in somewhatless than 5 seconds, thus applying an initially high power level to theload but smoothly effecting a transition to a desired level of 6.3V.Curve B illustrates the voltage applied across the 79 load where V is126V. and R 71'), while curve C represents the results where V, is 10V.and R is 4.49. In each instance curves B and C show decreases frominitial higher voltage levels to about 6.3V. after about 5-6 seconds.

FIG. 4 illustrates the reduction in potential across the filament orcathode heater of a typical CRT connected as load K in the circuit ofFIG. 1 where R is 79, V1 is 15.8 v.d.c. (curve E) and 12.6 v.d.c. (curveF), P1 is a 120C. pill, and P2 is an 80C. pill with a resistance of [.20at ambient. It will be noted that, because of the lower cathode heaterresistance when cold, the voltage across the heater initially rises asthe cathode heater temperature and resistance rise, then as the cathodeheater resistance stabilizes at its S-Jfl level, this voltage peaks anddecreases to the desired level of about 6.3V. at which level the heaterof the CRT cathode will be maintained at its desired temperature. thusproviding accelerated heating of the cathode so that a picture will beprovided in about 5-7 seconds after turn-on. It will be noted that thetransition of voltage from that initially applied to the reduced butnormal level is always smooth in contradistinction to that which wouldoccur if switching were employed to reduce an initial high level to thesteady-state operating level.

While PTC resistor P1 preferably has a somewhat higher stabilizationtemperature, it is to be understood that similar PTC pills having thesame temperatures of stabilization may be used. In either event it willbe noted that PI, the heater pill, by being connected across the entirepotential of V, will self-heat more rapidly than will P2. Thus P1supplies a substantial heat input to P2 and causes it to increase itstemperature and resistance more rapidly than it would if it was heatedonly by its own self-heating. It will also be noted that more complextypical time delay circuitry is entirely eliminated and only inexpensiveconventional PTC pills and standard fixed resistors are employed in theapparatus of this invention.

FIG. 3 illustrates another embodiment of this inven- 5 tion where Plperforms a second function. In this appa ratus PI is series connectedwith a conventional degausser coil D of the color television receiver,and a second voltage V2 is applied to P1 and D through a second set ofcontacts of a double-pole switch S1. Usually line voltage of about 118V.is utilized for V2 so that for a brief initial few seconds after closingof S1 relatively high voltage is applied across coil D (which typicallyhas an impedance of 5-1 ID) to effect degaussing. Very rapidly, however,the fast rising temperature and resistance of P1 reduce the voltageacross D and the current so that it is substantially deenergized duringcontinued operation of the television receiver. Upon turning off thereceiver, P1 and P2 cool so that after a very brief period, reactuationof S1 will again effect accelerated heating of the cathode of the CRTand degaussing of the receiver when switch S is reclosed.

It will also be noted that P2 will be held at an elevated temperaturewhich is a function of the stabilization temperature of P1 and thecoefficient of heat transfer therebetween as well as the dissipationcharacteristics. Thus, if a 120C. or 135C. PTC pill is utilized for P1.the temperature of P2 may be held at a temperature higher than that atwhich it would stabilize if no heat were supplied from P1. For example,if P2 were an 80C. pill and P1 were a lC. or l35C. pill the steady-statetemperature of P2 may be 95l00C. or even higher and thus provide aresistance greater than what it would provide at its own stabilizationtemperature of 80C.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above constructions withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:

1. Apparatus for accelerating the heating of the cathode heater ofacathode ray tube or the like comprising:

a first self'heating positive temperature coefficient resistor having arelatively low initial resistance which increases abruptly as itstemperature rises above a given level;

means for interconnecting said resistor to an electrical power sourcethereby rapidly to heat it above said given level;

a second self-heating positive temperature coefficient resistorpositioned in heat-exchange relationship with said first resistor andhaving a relatively low initial resistance which increases abruptly asits temperature rises above a given level;

a resistor of substantially fixed resistance shuntconnected with saidsecond self-heating resistor; and

means for interconnecting said shunt-connected resistors in series withthe heater of said cathode across an electrical power source adapted tosupply power of a substantially constant potential in excess of thatrequired to maintain the heater of said cathode at a predeterminedtemperature.

the resistance of the second self-heating resistor being notsubstantially more than that of the fixed resistor at temperatures belowits aforesaid given level but substantially greater than that of thefixed resistor at temperatures above its aforesaid given level, wherebyafter power is initially supplied to the cathode heater its potentialwill be reduced from a level substantially in excess of that required tomaintain the heater at said predetermined temperature to a level whichmaintains the heater at substantially said predetermined temperature asthe first and second resistors self-heat thereby to increase and thenmaintain said second resistor at a temperature above its aforesaid givenlevel. 2. Apparatus as set forth in claim I wherein the firstself-heating resistor has a higher temperature at which its resistancestabilizes than has the second self-heating resistor.

3. Apparatus as set forth in claim 1 wherein the first self-heatingresistor is series-connected with a degaussing coil across the firstmentioned said electrical power source, and which includes switchingmeans for concurrently energizing the first and second self-heatingresistors from respective electrical power sources thereby initially toenergize the degaussing coil for a brief period of time while the firstself-heating resistor rapidly heats and raises the temperature of thesecond self-heating resistor.

4. Apparatus as set forth in claim I wherein both the first mentionedand second mentioned said electrical power sources are constituted by asingle common power source.

1. Apparatus for accelerating the heating of the cathode heater of acathode ray tube or the like comprising: a first self-heating positivetemperature coefficient resistor having a relatively low initialresistance which increases abruptly as its temperature rises above agiven level; means for interconnecting said resistor to an electricalpower source thereby rapidly to heat it above said given level; a secondself-heating positive temperature coefficient resistor positioned inheat-exchange relationship with said first resistor and having arelatively low initial resistance which increases abruptly as itstemperature rises above a given level; a resistor of substantially fixedresistance shuntconnected with said second self-heating resistor; andmeans for interconnecting said shunt-connected resistors in series withthe heater of said cathode across an electrical power source adapted tosupply power of a substantially constant potential in excess of thatrequired to maintain the heater of said cathode at a predeterminedtemperature; the resistance of the second self-heating resistor beingnot substantially more than that of the fixed resistor at temperaturesbelow its aforesaid given level But substantially greater than that ofthe fixed resistor at temperatures above its aforesaid given level,whereby after power is initially supplied to the cathode heater itspotential will be reduced from a level substantially in excess of thatrequired to maintain the heater at said predetermined temperature to alevel which maintains the heater at substantially said predeterminedtemperature as the first and second resistors self-heat thereby toincrease and then maintain said second resistor at a temperature aboveits aforesaid given level.
 2. Apparatus as set forth in claim 1 whereinthe first self-heating resistor has a higher temperature at which itsresistance stabilizes than has the second self-heating resistor. 3.Apparatus as set forth in claim 1 wherein the first self-heatingresistor is series-connected with a degaussing coil across the firstmentioned said electrical power source, and which includes switchingmeans for concurrently energizing the first and second self-heatingresistors from respective electrical power sources thereby initially toenergize the degaussing coil for a brief period of time while the firstself-heating resistor rapidly heats and raises the temperature of thesecond self-heating resistor.
 4. Apparatus as set forth in claim 1wherein both the first mentioned and second mentioned said electricalpower sources are constituted by a single common power source.